1. Field of the Invention
The present invention relates to a spray applicator for spraying reactant mixtures, such as polyurethane mixtures of polyol and isocyanate that may also be combined with coloring agents and other additives. The spray applicator also includes fluid ports for flushing and purging reactant mixtures from the applicator.
2. Background Art
Spray polyurethane processes are currently being developed for spray forming articles of manufacture, such as interior trim assemblies for vehicles. Polyurethane is normally formed by mixing polyol and isocyanate in a spray gun or applicator mix head. Polyol and isocyanate react relatively quickly to form polyurethane and, therefore, must be mixed just prior to dispensing or they may react and clog the spray gun or applicator mix head. Polyurethane is generally off-white, black, or gray in color. In many applications, it would be advantageous to provide a desired color in the polyurethane that is used to spray form articles of manufacture. This may be true even if the article has a pigmented in-mold coating that covers the exterior of the spray formed article.
Products formed by polyurethane spray forming processes can benefit from supplying additives to the polyol and isocyanate mixture. Examples of additives that increase the utility of polyurethane spray foam products include blowing agents for forming foam polyurethane, color concentrates for coloring the finished product, and cell opener polyol compounds that can soften the polyurethane.
Spray form polyurethane can be used to form a durable exterior surface skin layer and also form a polyurethane foam layer that may form a foam backing for a polyurethane skin. A blowing agent or cell opening polyol may be combined with polyol and isocyanate to form a foam layer behind a skin layer that can be used to form a covered padded portion of an interior trim assembly. Prior systems for forming a padded polyurethane portion of an interior trim component requires two separate spray applicators or spray guns. One spray applicator would be used to form the polyurethane skin, while a second spray applicator would be used to form the polyurethane foam layer. Either applicator could be provided with a colorant additive that mixes color with the polyol prior to being provided to the spray applicator. Use of multiple spray applicators increases the process time and material waste due to the need to more frequently flush the spray applicators with solvent to purge reactant materials from the spray applicator. Changing from one spray applicator to another requires added processing time and reduces productivity.
It would be beneficial to develop a system and apparatus for a spray forming polyurethane process wherein different additives may be added selectively at different points in the spray forming process. It would also be advantageous to provide a spray forming head that can selectively provide additives that may color, condition or foam the polyurethane in predetermined portions of a spray formed article.
There is also a need for a spray applicator having built-in solvent flush and air purge ports that can be used to readily and rapidly clear any constituents used to form the polyurethane article from the spray applicator.
The above problems and short-comings of the prior art are addressed by applicants' invention as summarized below.